I’ve found it best not to retune at times of high atmospheric pressure (due to better signal propagation?) otherwise I sometimes get channels from adjacent TV regions which may actually be stronger than my local region. The evening tends to be the best time of day.

To answer this question properly a knowledge of which transmitters are involved and which UHF channels they use to transmit the digital MUX available from each transmitter.

If you understand the following it will help greatly to see what is going on.

The UHF band in the UK nominally spans UHF channels 21 – 68 (do not confuse with the channel numbers you see on the epg. These are properly called logical channel numbers (lcn’s). These are allocated by whatever epg you use and is not part of the actual video/audio (Frequently confuses satellite box owners using non-freesat mode who expect consistant lcn’s). The higher number UHF channels are no longer used for TV in the UK – the government sold them to the highest bidder for use by other services eg 4G mobile services (The so called Digital Dividend).

The same uhf carriers were used for the previous analogue (PAL) colour TV service and now for Digital TV/Radio services (DVB/DVB-T2).

The key item of info is :

Analogue – One UHF channel (properly called a carrier) carries just one TV channel.

Digital – One carrier has multiple TV and/or radio channels digitally mixed together. The mixing is properly known as multiplexing, hence the specific carrier is known as a MUX for terrestrial sources. (Digital satellite uses a basically similar system but the carrier used for a MUX is called a transponder).

When you autotune a terrestrial digital TV/box, the box starts looking for channels at UHF 21 and works it way up to 68. When it finds receivable channels (even weak ones), it stores the channels using the lcn’s allocated by the epg. Let’s say for example the particular channels it finds includes BBC 1 (SD) which it stores as lcn 1. Now imagine on it’s way up the UHF band it finds a second version of BBC 1 SD, lcn 1 is already used so it allocates a locally generated lcn starting from 801 (could be 800). The next duplicate gets 802 and so on.

Assuming there are just two transmitters in range (more gets even more complicated), there are 3 possibilities.

1 The unwanted transmitter has all it’s mux using lower UHF carriers

2 The unwanted transmitter has all it’s mux using higher UHF carriers

3 The unwanted transmitter and the wanted one UHF carriers overlap.

In the case of 1 – all your wanted channels are at 801 and up

In the case of 2 – all your wanted channels are at the correct lcn’s, unwanted ones are at 800 and up.

In the case of 3 the epg is a mess, some of the wanted ones are at the correct lcn’s, others are at 800 and up.

Hopefully you will now appreciate that only in the case 2 is it simply possible to delete the channels over 800.

Basically it’s much simpler to advise ditch the lot and manually tune. After doing it a couple of times it’s a very simple procedure.

Armed with the above info and easily obtained channel numbers used by the transmitters involved, you might want out of interest to look at your specific location to see where the desired channels finished up.

I always prefer to tune manually as I am in control.

I know the channels on which my transmitter broadcasts (see https://ukfree.tv/transmitters/tv/Mendip or http://www.digitaluk.co.uk/home) and I manually tune only those I want (from C49 for BBC, C54 for commercial, C58, C48, C56, C52, C51, C33 and C35) which ensures I miss all 800 channels from local repeaters, Welsh transmitters and, in exceptional conditions, distant transmitters.

That being said, the FVP seems much better at Automatic tuning than the 9200T – or it may be that Freeview transmitted meta-data now includes data about which channels come from which transmitter.